1. Field of the invention
The present invention relates, in general, to a printed circuit board (PCB) including an embedded passive component and a method of fabricating the same and, more particularly, to a PCB including an embedded passive component, in which the passive component is mounted in a predetermined receiving hole for communicating with via holes, and in which walls of the via holes are used as terminals connected to electrodes of the passive component, and a method of fabricating the same.
2. Description of the Prior Art
Recently, electronic technologies are moving toward the embedding of resistors, capacitors, integrated circuits (IC) or the like into a substrate so as to cope with demand for miniaturization and sophisticated functions of electronic goods according to advances in the electronics industry.
Typically, discrete chip resistors or discrete chip capacitors have been frequently mounted on most PCBs, but, recently, PCBs are developing in which passive components, such as resistors or capacitors, are embedded.
In other words, a technology for fabricating the PCBs including the passive components embedded therein, achieves substitution of conventional chip resistors or chip capacitors by mounting the passive components on an external part of a PCB or in an internal part of the PCB according to a novel process employing a novel material.
The PCB including the passive component embedded therein has a structure in which the passive component is mounted on the external part of the PCB or embedded in the internal part of the PCB, and if the passive component is integrated with the PCB to act as one part of the PCB regardless of the size of the PCB, the passive component is called an “embedded (buried) passive component” and the resulting PCB is called “printed circuit board including embedded passive component”.
One of the most important features of the PCB including the passive component embedded therein is that since the passive components such as resistors or capacitors are already mounted as part of the PCB in the PCB, it is not necessary to mount additional passive components on a surface of the PCB.
FIGS. 1a to 1f are sectional views illustrating the fabrication of a conventional PCB including an embedded passive component, which is disclosed in Japanese Pat. Laid-Open Publication No. 2002-118366.
As shown in FIG. 1a, a groove 111 is formed on a core substrate 110 having a predetermined circuit pattern, and an adhesive 112 is applied to the bottom of the groove 111.
As shown in FIG. 1b, a chip capacitor 120 adheres to the bottom due to the adhesive 112.
As shown in FIG. 1c, a thermosetting resin is packed in the groove 111, heated and hardened to form a resin layer 113.
As shown in FIG. 1d, a thermosetting epoxy-based resin sheet is laminated on the core substrate 110, and then vacuum-pressed at 50-150° C. at a pressure of 5 kg/cm2 to form a resin insulating layer 114.
As shown in FIG. 1e, the resin insulating layer 114 is bored using a laser to form via holes 115 connected to first and second electrodes 121 and 122 of the chip capacitor 120.
As shown in FIG. 1f, the PCB 110 including the embedded passive components (or capacitors) is created using a typical PCB build-up method.
In the conventional PCB 110 including the embedded passive component fabricated according to a procedure of FIGS. 1a to 1f, the via holes 115 connected to upper or lower sides of the first and second electrodes 121 and 122 must be formed to electrically connect a passive component chip (i.e. capacitor chip 120). However, since the upper or lower sides of the first and second electrodes 121 and 122 have a very small surface area, it is difficult to form the via holes 115.
Due to such a difficulty of formation of the via holes 115, the conventional PCB 110 including the embedded passive component is problematic in that portions of the via holes 115 are apt to be formed on a portion other than surfaces of the electrodes 121, 122, resulting in a short circuit, and in that the via holes 115 may not be connected to the electrodes 121, 122.
In conjunction with the above process in which the groove is formed on the PCB and the passive component is mounted in the groove, another process has been developed, in which passive components are laminated on both sides of an internal substrate.
FIGS. 2a to 2g are sectional views illustrating the fabrication of a conventional PCB including embedded passive components, which is disclosed in Japanese Pat. Laid-Open Publication No. 2004-146495.
As shown in FIG. 2a, a copper clad laminate 210 is provided, which includes a core substrate 211 and copper foil layers 212. Predetermined through holes 213 are already formed through the copper clad laminate.
As shown in FIG. 2b, the upper and lower copper foil layers 212 of the copper clad laminate 210 are etched to form circuit patterns 214.
As shown in FIG. 2c, chip capacitors 220 adhere to the copper clad laminate 210 due to an adhesive.
As shown in FIG. 2d, conductive pastes 215 are applied according to a screen printing process to electrically connect electrodes at the sides of the chip capacitors 220 to the circuit patterns 214.
As shown in FIG. 2e, insulating layers 230 are formed on both sides of the substrate so as to embed the chip capacitors 220.
As shown in FIG. 2f, resin coated coppers (RCC) 240 in which resins 241 are applied on copper foils 242 are laminated on both sides of the substrate.
As shown in FIG. 2g, the PCB 200 including the embedded passive components (or capacitors) is created adopting a typical PCB build-up method.
The conventional PCB 200 including the embedded passive components fabricated according to a procedure of FIGS. 2a to 2g is problematic in that since the application of the conductive pastes 215 is implemented using the screen printing process in which there is a large tolerance, a short circuit readily occurs between the fine circuit patterns. This brings about an undesired electrical connection between the electrodes of the embedded passive components (i.e. chip capacitors 220) and circuit patterns, resulting in reduced reliability of the electronic goods.